The tetanic depression in fast motor units of mammalian skeletal muscle can be evoked by lengthening of one initial interpulse interval

A lower than expected tetanic force (the tetanic depression) is regularly observed in fast motor units (MUs) when a higher stimulation frequency immediately follows a lower one. The aim of the present study was to determine whether prolongation of only the first interpulse interval (IPI) resulted in tetanic depression. The experiments were carried out on fast MUs of the medial gastrocnemius muscle in cats and rats. The tetanic depression was measured in each case as the force decrease of a tetanus with one IPI prolonged in relation to the tetanic force at the respective constant stimulation frequency. Force depression was observed in all cases studied and was considerably greater in cats. For cats, the mean values of force depression amounted to 28.64% for FR and 10.86% for FF MUs whereas for rats 9.30 and 7.21% for FR and FF motor units, respectively. Since the phenomenon of tetanic depression in mammalian muscle is commonly observed even after a change in only the initial interpulse interval within a stimulation pattern, it can effectively influence processes of force regulation during voluntary activity of a muscle, when motoneurones progressively increase the firing rate

Reactive oxygen species and male reproductive hormones

Reports of the increasing incidence of male infertility paired with decreasing semen quality have triggered studies on the effects of lifestyle and environmental factors on the male reproductive potential. There are numerous exogenous and endogenous factors that are able to induce excessive production of reactive oxygen species (ROS) beyond that of cellular antioxidant capacity, thus causing oxidative stress. In turn, oxidative stress negatively affects male reproductive functions and may induce infertility either directly or indirectly by affecting the hypothalamus-pituitary-gonadal (HPG) axis and/or disrupting its crosstalk with other hormonal axes. This review discusses the important exogenous and endogenous factors leading to the generation of ROS in different parts of the male reproductive tract. It also highlights the negative impact of oxidative stress on the regulation and cross-talk between the reproductive hormones. It further describes the mechanism of ROS-induced derangement of male reproductive hormonal profiles that could ultimately lead to male infertility. An understanding of the disruptive effects of ROS on male reproductive hormones would encourage further investigations directed towards the prevention of ROS-mediated hormonal imbalances, which in turn could help in the management of male infertility

Assessment of postural stability in patients with lumbar spine chronic disc disease

Purpose: The pain, motor and sensory deficits are common symptoms of the lumbar disc disorder, and they can significantly affect human postural control. The aim of this study was to assess postural stability in patients with severe symptoms of lumbar spine disc disease qualifying them for surgical treatment and to compare them with a control group. Methods The study involved 103 subjects: 54 patients and 49 healthy subjects. Patient’s mean age was 46.4 ± 11.3 years, mean body height 172.2 ± 10.3 cm, mean body mass was 83.1 ± 18.9 kg and mean body mass index (BMI) was 27.9 ± 5.2 kg m-2. The mean time of their recent pain episode was 9.7 ± 8.5 month. Results: We found statistically significant differences between postural stability in patients with lumbar spine disc disease and the control group. The measurements taken with eyes closed, as compared with the clinical control group, revealed higher and statistically significant values of the mean amplitude of COP, mean amplitude of COP on sagittal plane, and maximal sway in sagittal plane parameters. The analysis of pressure value differences between the right and left lower limbs in both groups revealed statistical significance. In the study population the difference was significantly greater in comparison to the control group. The patients has significantly greater asymmetry of lower limb load. Conclusions: 1. Patients with lumbar spine discogenic pain had decreased postural control. 2. The patients had significant asymmetry in foot pressure, resultant from pain radiating to a lower limb

Mikrostruktura stopów NiAlV poddanych odkształceniu metodą skręcania pod wysokim ciśnieniem

Some attention in physical metallurgy is devoted to the mechanisms of decomposition of the disordered phases via eutectoid transformation accompanied by the atomic ordering. In case of the non-pearlitic modes of transformation this concerns intermetallic phases of the general description A3B-A3C. The application of intensive deformation like HPT may introduce opposite mechanisms introducing some degree of the metastable disordered phase structure at room temperature. The paper presents results of the phase composition and microstructure studies of the alloys of composition Ni75AlxVy (where x =15, 10, 5 and y =10, 15, 20), which undergo the solid-state eutectoid decomposition at temperature 1281 K, in the equilibrium conditions. The alloys achieved by the cold crucible levitation method were later intensively deformed with the method of high pressure torsion (HPT). The alloys after HPT revealed homogenous, metastable L12 (Ni3Al) structure in place of the eutectoid product L12-D022. The average size of the Sherrer’s coherent diffraction volumes did not exceed 9 nm, suggesting nano-structure of the material. Transmission electron microscopy (TEM) and high resolution electron microscopy (HRTEM) revealed that the micro- and nano- deformation twins were the main feature of the microstructure, dividing volume into cells of the sizes similar to the coherent volumes. The HPT deformation did not influence atomic order. The results are compared with those achieved for the injection cast samples.W publikacjach z zakresu fizycznej metalurgii przejawia się zainteresowanie mechanizmami rozpadu, nie perlitycznego typu, faz nieuporządkowanych, zachodzącymi z udziałem uporządkowania atomowego. Dotyczy to faz rodzaju A3B-A3C. Zastosowanie intensywnego odkształcenia metodą skręcania pod wysokim ciśnieniem (HPT) może przeciwdziałać rozpadowi wprowadzając fazy metastabilne, o pewnym stopniu nieuporzadkowania atomowego, w temperaturze pokojowej. Artykuł przedstawia wyniki badań składu fazowego i mikrostruktury stopów o składzie Ni75AlxVy (gdzie x =15, 10, 5 i y =10, 15, 20), podlegających, w warunkach równowagi, rozpadowi eutektoidalnemu w temperaturze 1281 K. Stopy otrzymano metodą lewitacji w zimnym tyglu (CCLM) a następnie poddano przeróbce metodą intensywnego odkształcenia skręcaniem pod wysokim ciśnieniem. Po takim procesie stopy wykazywały jednorodną strukturę L12 (Ni3Al), zamiast produktów rozpadu eutektoidalnego w postaci struktur L12-D022. Średni rozmiar koherentnych obszarów rozpraszania Sherrera nie przekraczał 9 nm, wskazując na materiał o charakterze nano-strukturalnym. Zastosowanie transmisyjnej mikroskopii elektronowej (TEM) i wysokorozdzielczej transmisyjnej mikroskopii elektronowej (HRTEM) pokazało, że bliźniaki odkształcenia o rozmiarach mikro i nano były głównymi elementami mikrostruktury, dzieląc całą objętość na komórki o rozmiarach podobnych do rozmiarów obszarów koherentnego rozpraszania. Metoda HPT nie wpłynęła natomiast na uporzadkowanie atomowe. Wyniki porównano z uzyskanymi dla próbek otrzymanych metodą szybkiego chłodzenia przez wtryskiwanie do wlewnicy

Interfacial reactions and microstructure related properties of explosively welded tantalum and steel sheets with copper interlayer

This paper presents a comprehensive study of the microstructure-property relationships in Ta and stainless or carbon steel composites, fabricated by explosive welding using Cu interlayer. Employing scanning (SEM) and transmission (TEM) electron microscopy and X-ray synchrotron diffraction, a complex microstructure of interfacial layers was examined. Particular attention was placed on the description of the phase transformation mechanisms in the reaction regions, and the competition between the strain-hardening and softening processes in parent sheets. SEM and TEM analyses showed that Cu and Ta nanoparticles, and small dendrites, dominated the reaction regions near the Ta/Cu interfaces, whereas the nano-grained phases having more complex chemical compositions were identified near the Cu/steel interfaces. SEM orientation mapping revealed that the interfacial layers of the parent sheets underwent severe plastic deformation as a result of dislocation slip, twinning, and shear banding. Such heavily deformed areas can easily undergo recovery and recrystallization already during clad processing. In consistence with these findings, the micro-hardness values of the welded sheets increased as the joining interface approached, except for the layers directly adhering to large reaction regions, where a decrease in micro-hardness was observed. However, the solidified melt regions were essentially softer than the strain-hardened layers of both steels. Based on experimental results a new explanation for the reaction region formation was proposed and a significant modification of the description of the interfacial microstructure of parent sheets was done. Finally, the effect of microstructural changes on the clads properties was discussed